1. Field of the Invention
The present invention relates to a character display apparatus and a character display method capable of displaying an italic character with high quality using a color display device, and a recording medium for use with such apparatus and method.
2. Description of the Related Art
Italic characters are widely used for the purpose of displaying characters in an emphasized manner.
In a conventionally-known display technique for displaying characters on a display device, such as a liquid crystal display device, a cathode ray tube display device, etc., a bit map which represents the shape of a character is displayed by units of a pixel. The bit map which represents the shape of a character is, for example, a dot font.
The bit map defines the shape of a character by units of a dot. In the bit map, a dot corresponding to a portion of the character is represented by a bit having a value “1”, and a dot not corresponding to a portion of the character is represented by a bit having a value “0”. In this way, in the bit map, one dot is represented by information of one bit. The bit map includes bits which represent corresponding dots. In the present specification, dots represented by bits included in a bit map are referred to as “dots which form the bit map”.
As a conventional technique for displaying an italic character on a display device, a technique for displaying an italic character on a display device based on a bit map stored in a memory of a character display apparatus (e.g., computer) which represents the italic character is known.
FIG. 41 shows an example of an italic character displayed on a display device based on a bit map which represents an italic character of a character “A” of the English language alphabet. In FIG. 41, each hatched box represents a pixel displaying black and each open box represents a pixel displaying white.
In this conventional technique, it is necessary to store bit maps which represent italic characters in a memory of a character display apparatus in addition to bit maps of normal (non-italic) characters which are usually stored in the character display apparatus.
Another conventional technique for displaying an italic character on a display device is disclosed in Japanese Laid-Open Publication No. 59-60474. In this conventional technique, the shape of a non-italic character is represented by a bit map, and dots which form a bit map correspond to pixels of the display device in a one-to-one manner. In this technique, a bit map which represents the shape of a character is deformed by units of a dot (i.e., by units of a pixel) so as to generate a bit map which represent an italic version of the character, and each pixel of the display device is controlled between black and white based on the bit map which represent the italic character, whereby an italic character is displayed. Thus, it is not necessary to previously store bit maps which represent italic characters in a memory.
Since dots which form a bit map that represents the shape of a non-italic character correspond to pixels of the display device in a one-to-one manner. The shape of a non-italic character is defined by units of a pixel.
Hereinafter, in the present specification, a bit map which defines the shape of a non-italic character or an italic character by units of a pixel is referred to as a “bit map defined by units of a pixel”. A non-italic character is simply referred to as a “character”.
FIG. 42A shows an example of a character “H” of the English language alphabet displayed on a display plane 900 of 16 pixels×16 pixels based on a bit map defined by units of a pixel. In FIG. 42A, each hatched box represents a pixel displaying black and each open box represents a pixel displaying white.
FIG. 42B shows an example of an italic character “H” of the English language alphabet displayed on the display plane 900 based on a bit map obtained by deforming the bit map of FIG. 42A defined by units of a pixel.
In the examples illustrated in FIGS. 42A and 42B, a bit map defined by units of a pixel is deformed according to the technique disclosed in Japanese Laid-Open Publication No. 59-60474 such that each of the dots which form the bit map are shifted along the X direction by a number of dots determined based on a distance from the bottom of the character. In this deformation example, as the distance from the bottom of the character is increased by 3 dots, the number of dots by which dots are shifted is increased by 1.
In this way, a bit map which defines the shape of a character by units of a pixel is deformed so as to generate a bit map which represents an italic character, whereby an italic character can be displayed on a display device without previously storing bit maps which represent italic characters in a memory.
In the conventional technique disclosed in Japanese Laid-Open Publication No. 59-60474 where a bit map which defines the shape of a character by units of a pixel is deformed so as to generate a bit map which represents an italic version of the character, “jaggedness” becomes more conspicuously in a character, especially in an italic character including an oblique line as a component of the character. As a result, the display quality of the italic character is deteriorated. In such a case, characters are difficult and unpleasant to read, which imposes eye strain on an observer of the display device.
FIG. 43A shows an example of a character “A” of the English language alphabet displayed on a display plane 900 of 16 pixels×16 pixels based on a bit map defined by units of a pixel. In FIG. 43A, each hatched box represents a pixel displaying black and each open box represents a pixel displaying white.
FIG. 43B shows an example of an italic character “A” of the English language alphabet displayed on the display plane 900 based on a bit map obtained by deforming the bit map of FIG. 43A defined by units of a pixel. As shown in FIG. 43B, the display quality of the italic character “A” is deteriorated in an oblique line of the character “A” (e.g., a portion 4201).
FIG. 44A shows another example of a character “A” of the English language alphabet displayed on a display plane 900 of 16 pixels×16 pixels based on another bit map defined by units of a pixel.
FIG. 44B shows another example of an italic character “A” of the English language alphabet displayed on the display plane 900 based on a bit map obtained by deforming the bit map of FIG. 44A. In FIG. 44B also, the display quality of the italic character “A” is deteriorated in the oblique lines of the character “A” (e.g., portions 4301 and 4302).
It is understood from FIGS. 43B and 44B that, according to the conventional technique, the display quality of a character is decreased also when the slant angle of an oblique line included in the character is changed.
Thus, the conventional technique includes the above-described problem of deterioration in the display quality of an italic character.